* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > Has anyone found a non-synthetic benchmark where this makes a > > significant difference? Aside from btrfs, I mean. > > Yea, if you have some particular filesystem (or other subsystem) that > uses a global mutex, you'll obviously see way more contention. Btrfs may > not be _unique_ in this regard, but it's definitely doing something that > isn't good. > > Btw, it's doing something that ext3 also used to do iirc, until we fixed > it to use spinlocks instead (the block group lock in particular). > > Yeah - just double-checked. Commit c12b9866ea52 in the historical Linux > archive, from 2003. Which made block allocation protected by a per-group > spinlock, rather than lock_super(). btw., i think spin-mutexes have a design advantage here: in a lot of code areas it's quite difficult to use spinlocks - cannot allocate memory, cannot call any code that can sporadically block (but does not _normally_ block), etc. With mutexes those atomicity constraints go away - and the performance profile should now be quite close to that of spinlocks as well. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
